1. Field of the Invention
This invention relates to a fuel control device for an internal combustion engine provided with an air flow quantity sensor, which detects failure in the air flow quantity sensor, supplies fuel to the engine based on a preset intake air quantity when the air flow quantity sensor fails and informs the vehicle driver of the failure.
2. Discussion of Background
An electronically controlled fuel injection device which has rapidly been installed in an automobile in recent time is a device for making a mixture supplied to a combustion chamber of the engine, which converts a revolution number or an intake air quantity or the like to electric signals, processes these signals by a microcomputer, and generates a signal signifying an optimum air fuel ratio. The device controls the air fuel ratio by controlling valve opening time of fuel injection valves which are electromagnetically driven by these signals, to thereby keep optimizing operational state of the engine.
Generally, in such an electronically controlled fuel injection device of this kind, an air flow quantity sensor is installed at an intake air passage of the engine. For instance, the device calculates an intake air quantity per intake stroke, Q/N based on an intake air flow quantity per unit time Q which is measured by the air flow quantity sensor, and a number of intake times per unit time N, and supplies the fuel quantity which is obtained from a target fuel air ratio and the intake air quantity Q/N from fuel injection valves to the engine.
Conventionally, in detecting failure such as damaged parts in the air flow quantity sensor, or incomplete wiring contact, or an erroneous operation thereof or the like, the air flow quantity per unit time and a predetermined value time are compared, and the air flow quantity sensor is determined as failed in case that a measured value of the air flow quantity is smaller than a predetermined value on the lower limit side, or in case that the measured value of the air flow quantity is larger than a predetermined value on the upper limit side.
Since the failure detection of the conventional air flow quantity sensor is performed as above, the failure determination can be performed only in case that an output of the air flow quantity sensor is extremely abnormal. Therefore, a failure to an extent wherein an output error of the air flow quantity sensor is enlarged due to deterioration of inner parts of the air flow quantity sensor or loose contact of connector portions thereof or the like, is not determined as a failure, which causes increase of injurious components in exhaust gas, knocking, and melting loss of an exhaust system of the engine due to temperature elevation of the exhaust gas.